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In neuropsychology, equipotentiality is a neurological principle that describes a cortical mechanism, first identified by Jean Pierre Flourens and later revisited by Karl Lashley in the 1950s. The principle of equipotentiality is the idea that the rate of learning is independent of the combination of conditioned and unconditioned stimuli that are used in classical conditioning.

After performing ablation experiments on birds, and seeing that they could still fly, peck, and perform a range of other regular behaviours, Flourens concluded that every area of the brain was capable of doing what every other area of the brain could, but only for higher-level functions which he called 'perception'. He also argued that elementary sensory input was localized, which is supported by current research. The famous saying that we only use 10% of our brains originates from Flourens, back about a century and a half ago.

Lashley offered two generalizations from his research, that recently have been successfully challenged but nonetheless represent important milestones in the development of neurological theory:

Although surgical removal of a portion of the cortex can produce significant behavioral deficits, those deficits can be recovered through additional training and time, by way of the development of new neuronal connections. Lashley argued that the brain is sufficiently plastic, such that when one region of the brain is surgically removed (or damaged through injury) another region takes over the damaged region's function. This is the principle Lashley referred to as equipotentiality. Extensive regions of the cerebral cortex have the potentiality for mediating specific learning and memory functions.

His principle of "mass action" stated that the cerebral cortex acts as one—as a whole—in many types of learning.

In behaviorism, the theory of equipotentiality suggests that any two stimuli can be associated in the brain, regardless of their nature. It proposes that all forms of associative learning, both classical (Pavlovian) and operant (Skinnerian) involve the same underlying mechanisms. However, food avoidance experiments have questioned its application.